1. Field of the Invention
The present invention generally relates to techniques for improving computer system performance. More specifically, the present invention relates to instructions that prevent structural hazards associated with conditional data dependencies during vector or parallel-processing operations.
2. Related Art
There are many impediments to the parallelization of computational operations in parallel-processing systems. Among these impediments are data dependencies, such as data dependencies that carry across iterations of a loop (which are sometimes referred to as loop-carried dependencies). In existing parallel processing systems, it is typically assumed that loops that include loop-carried dependencies cannot be vectorized or implemented in parallel unless the dependencies are predictable, such as the value of a loop-index variable.
In existing computer systems, a compiler may identify loop-carried dependencies that are related to the structure of the code and that can be determined when the code is compiled, which are henceforth referred to as structural hazards. (Note that these structural hazards are distinct from memory hazards, such as address hazards, in which different memory references refer to the same address). Typically, structural hazards are conditional in nature, i.e., a loop-carried dependency may or may not arise because the loop-carried dependency may depend on the state of a condition variable. Because the state of the condition variable cannot be known when the code is compiled, the compiler typically takes the most conservative approach and does not vectorize in the presence of a possible loop-carried dependency, even though the loop-carried dependency may never actually occur.
Hence, what is needed is a technique to facilitate vector or parallel processing in the presence of structural hazards without the above-described problems.